Method for the recovery of gallium using an alkali metal amalgam



June 14, 1966 K. BIELFELDT ETAL 3,256,086

METHOD FOR THE RECOVERY OF GALLIUM USING AN ALKALI METAL AMALGAMOriginal Filed June 19, 1962 3 Sheets-Sheet 1 June 1966 K. BIELFELDTETAL 3,256,086

METHOD FOR THE RECOVERY OF GALLIUM USING AN ALKALI METAL AMALGAMOriginal Filed June 19, 1962 s Sheets-Sheet 2 June 1966 K. BIELFELDTETAL 3,

METHOD FOR THE RECOVERY OF GALLIUM USING AN ALKALI METAL AMALGAMOriginal Filed June 19, 1962 Z5 Sheets-Sheet 5 Fig. 3

Jn van/01's A fazw 43/14/35 0: I %Q ZaJ ao rer United States Patent s256 086 METHOD FOR THE REOVERY 0F GALLIUM USING AN ALKALI METAL AMALGAMKlaus Bielfeldt and Max Laspeyres, Schwandorf, Germany, assignors toVereinigte Aluminium-Werke Aktiengesellschaft, Bonn, Germany Originalapplication June 19, 1962, Ser. No. 203,597. Divided and thisapplication Oct. 22, 1963, Ser. No. 318,060 Claims priority, applicationGermany, Aug. 12, 1959,

V 17,063; June 21, 1961, V 20,840 15 Claims. (Cl. 75-121) The presentapplication is a division of our copending application Serial No.203,597, filed June 19, 1962 and entitled Method and Apparatus for theRecovery of Gallium. Application Serial No. 203,597 is acontinuation-in-part of our application Serial No. 48,578, filed August10, 1960, now abandoned, and entitled Method for the Recovery of GalliumFrom Gallium-Containing Solutions.

The present invention relates to a method for the recovery of galliumfrom gallium-containing solutions and more particularly, the presentinvention is primarily concerned with the recovery of gallium fromsodium aluminate solutions, such as form an intermediate product in therecovery of aluminum hydroxide from bauxite.

It is well known that the alkaline sodium aluminate solutions which areused in the recovery of aluminum hydroxide from bauxite will containincreasing quantities of such impurities or additional constituents ofthe bauxite which are dissolved together with the aluminum oxide oraluminum hydroxide and which upon decomposition of the solution will notbe precipitated together with the aluminum hydroxide. One of thecompounds which is dissolved in the alkaline aluminate solution andwhich does not precitate together with the aluminum hydroxide is sodiumgalliumate.

Many attempts have been made to utilize the enrichment of the aluminatesolution with galliumate for the recovery of gallium.

In this connection, it has been suggested to carry out precipitation ofthe aluminum hydroxide under such conditions that the residual solutionor mother liquid will retain the galliumate. Thereby, precipitation ofthe aluminum hydroxide can be carried out with acids or so as to producefor instance calcium aluminate or cryolite.

It was also suggested to separate gallium electrolytically by subjectingthe galliumate-containing sodium aluminate solution to electrolysis witha cathode consisting of moving liquid mercury and with one or moreanodes made of a metal which under the conditions prevailing during theelectrolysis remains insoluble. In this case, a terminal voltage of atleast 3 volts, for instance between 3.8 and 4.2 volts or preferablybetween 3.8 and 4.0 volts is required and the cathode potential is to beat least 1.6 volts and preferably between 1.9 and 2.2 volts,- while thecurrent density at the cathode must be at least 0.35 ampere per 100 cm.and preferably between 0.45 and 0.6 ampere per 100 cm. The gallium willbe dissolved in the cathodic mercury and can be recovered therefrom bymeans of a hydroxide of an alkali metal and the thus obtained alkalimetal galliumate solution can then be electrolyzed in known manner witha solid cathode so as to obtain thereon a precipitation of metallicgallium.

However, the first mentioned method has the decisive disadvantage thatthe entire process is highly complicated and that the major portion ofthe sodium hydroxide is destroyed during the process. Furthermore, it isnot possible to incorporate the first mentioned method into the overallarrangement of the Bayer process, i.e. into a process wherein bauxite isdigested with a caustic soda solution which dissolves the alumina andfrom which various oxides (but not gallium compounds) can beprecipitated, whereupon the solution is filtered and the alumi numcontained in the solution is precipitated as hydroxide.

The last mentioned method can be carried out without loss of the sodiumhydroxide and can be arranged within the Bayer process. However, theelectrolysis requires very considerable time and large quantities ofmercury' so that the last mentioned process too is not of the desiredsimplicity and low cost.

It is therefore an object of the present invention to overcome thedisadvantages and difiiculties which are inherent in the prior artmethods.

It is a further object of the present invention to provide a method forthe recovery of gallium from gallium-containing solutions which can becarried out in a simple and economical manner.

It is another object of the present invention to provide a simple andeconomical method of separating gallium from sodium aluminate solutionsand of recovering the separated gallium, which method can be carried outin a continuous manner and in conjunction with the working up of bauxiteor the like for the production of alumina.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description and of the appendedclaims.

With the above and other objects in view, the present inventioncontemplates in a method of recovering gallium from an alkaline solutionof a gallium compound, the

step of reacting the solution with an alkali metal. amalgam so as toreduce at least a portion of the gallium com-' pound to metallicgallium, the metallic gallium being taken up by the amalgam andsimultaneously transforming a portion of the alkali metal of the amalgaminto the hydroxide of the alkali metal the thus-formed hydroxide beingincorporated in the solution, whereby gallium is recovered from thesolution.

According to a preferred embodiment of the present invention, the sameis concerned with the recovery of gallium from an alkaline solutioncontaining alumina and gallium oxide by reacting droplets of liquidsodium amalgam having a diameter of between about 0.15 and 1.5 mm.

with the solution so as to reduce at least a portion of the dissolvedgallium oxide to metallic gallium, the latter being taken up by thesodium amalgam, while simultaneously incorporating a portion of thesodium of the sodium amalgam into the solution in the form of sodiumhydrox ide, separating the thus formed gallium-containing sodium amalgamfrom the solution, and recovering metallic gal-- lium from the amalgam.

The method of the present invention may be carried out in an arrangementwhich comprises reaction chamber means for reacting sodium amalgamwith agallium-containing solution so that at least a portion of the gallium ofsaid solution will be taken up by said amalgam in we change for aportion of the sodium thereof, thus forming a gallium-containing amalgamand a solution of reduced gallium content, separating means locatedabove and communicating with the reaction chamber means for receivingthe solution of reduced gallium content with a portion ofgallium-containing amalgam distributed therethrough and for separatingthe amalgam portion from the solution of reduced gallium content so thatthus-- separated amalgam will flow downwardly into the reaction chambermeans, conduit means communicating with The method of the presentinvention may also be carried out in an arrangement for recovery of afirst amalgam-forming metal from a solution thereof, which arrangementcomprises, in combination, reaction chamber means for reacting theamalgam of a second metal with a solution of the first metal so that atleast a portion of the first metal of the solution will be taken up bythe amalgam of the second metal in exchange for a portion of the secondmetal thereof, thus forming an amalgam containing the first metal and asolution containing a lesser proportion of the first metal and includinga portion of the second metal, the reaction chamber means comprising ahousing having an open upper and closed lower end portion, fluiddistribution means including a closed distribution chamber located inthe area of the upper end portion of the housing, and a plurality ofducts fluid permeable at their lower ends and spaced from each other,and communicating with, and extending downwardly from, the distributionchamber into the lower end portion of the housing, the reaction chambermeans further comprising means for introducing under pressure firstmetal-containing solution into the distribution chamber, and means forsubstantially filling the space within the housing between the spacedducts wit-h amalgam of the second metal so that the solution of thefirst metal will be forced from the distribution chamber through theducts into the lower portion of the amalgam filled space and will passupwardly through the same thereby reacting with the amalgam, so as toexchange first metal of the solution against second metal of theamalgam, separating means located above the reaction chamber means andincluding a downwardly converging bottom portion communicating with theupper end portion of the housing for receiving the upwardly passingsolution of reduced first metal content with a portion of firstmetalcontaining amalgam distributed therethrough, and .for gravityseparation of the amalgam portion from the solution of reduced firstmetal content so that the thus separated amalgam will fiow downwardlythrough the downwardly converging bottom portion of the separating meansinto the space in the reaction chamber, and extracting means operativelyconnected to the reaction chamber means for receivingfirst-metal-containing amalgam and for extracting first metal therefrom.

Thus, according to the present invention, gallium is recovered in asurprisingly simple and economical manner from an alkaline solution of agallium compound such as an alkaline solution containing alumina andgallium oxide by treating the aluminate lye with sodium amalgam. Therebythe amalgam reacts with the lye under reduction of the impuritiesdissolved in the lye so that the alkali concentration of the lyeincreases while gallium as well as other nobler metals will be reducedto their metallic state and will be taken up by the amalgam. Thereaction proceeds very quickly and up to 90% of the gallium can beeasily removed in this manner from the lye and will be taken up by themercury of the amalgam.

An additional difficulty of the above described prior art method for theelectrolytic recovery of gallium is found in the fact that the mercurywhich forms the cathode of the electrolytic process must form acontinuous body in order to allow for the passage of currenttherethrough. Consequently, the relationship between volume and surfaceof the mercury cathode is unfavorable for the formation of a largecontact area between the mercury and the electrolyte from which galliumis to be recovered. Furthermore, the moving and stirring of the mercurycathode must be carried out under carefully controlled conditions, sinceonly in this manner, i.e. in a carefully controlled operation, therequired renewal of the mercury surface can be achieved which isnecessary for the separation of gallium from the electrolyte. Incontrast thereto, according to the present invention as described above,it is possible to increase the surface area of. the sodium amalgampractically to any desired extent since it is no longer necessary tointroduce the mercury or to maintain the mercury as a continuous body.For instance, according to the present invention, the sodium amalgam canbe so strongly stirred while in contact with the aluminate lye that thesodium amalgam will be separated into relatively large droplets.According to a preferred manner of carrying out the present invention,the sodium aluminate lye is introduced into the sodium amalgam through aplurality of nozzles having relatively small orifices and, in thismanner, the amalgam will be separated into relatively small droplets.The relationship between surface area and volume changes in favor ofsurface area with decreasing size of the droplets and this again willspeed up the reaction and reduce the total quantity of mercury requiredfor carrying out the process to a fraction of the quantity of mercurywhich is needed according to prior art processes.

During the reaction between sodium aluminate lye and sodium amalgam inaccordance with the present invention, a portion of the sodium of thesodium amalgam will be converted into sodium hydroxide and will thenform part of the aluminate lye. Thus, at least a portion of the sodiumwhich is lost during the Bayer process will be replaced by sodiumhydroxide originating from the sodium amalgam. Thus, the formation ofsodium hydroxide according to the process of the present invention whichsodium hydroxide otherwise would have to be sup plied from an outsidesource, will compensate to a con siderable degree the electric energywhich is required for forming sodium amalgam which is used for thepresent invention. The sodium amalgam which is required for the presentprocess can be produced either in conventional manner from sodiumchloride, orand this has been found to be particularly advantageous andeconomical sodium carbonate, which is one of the waste products of thealumina production, can be used as the starting material for producingthe sodium amalgam.

The electrolytic separation of gallium in accordance with the abovedescribed prior art method, is preferably carried out in aluminate lyeor sodium aluminate solutions which contain between about and g. sodiumoxide per liter, since at higher concentrations the yield of gallium isgreatly reduced. It is a further advantage of the method of the presentinvention that sodium aluminate solutions of any desired concentrationcan be subjected to the process. Thus, it is possible withoutdifficulties to separate gallium from the heavy liquors of the Bayerprocess, i.e. from the highly concentrated solutions which are producedby partial evaporation and which are to be used for attacking newbauxite. These concentrated aluminate solutions contain usually about300 g. sodium oxide per liter.

The present process for the recovery of gallium can be incorporatedwithout difiiculties into the Bayer process for the recovery of alumina,and this can be done so as to recover gallium in a continuous manner.For instance, a portion of the evaporated aluminate solution or heavyliquor can be treated with sodium amalgam according to the presentinvention and thus freed of gallium, and the thus purified heavy liquorcan then be again combined with the portion of heavy liquor which hasnot been subjected to gallium separation. In this manner, the galliumconcentration in an aluminate solution can be maintained at a constantlevel by separating gallium in a quantity which corresponds to thequantity of gallium which is dissolved in the aluminate solution duringthe decomposition of bauxite.

A suitable arrangement of the apparatus required for carrying out theprocess will allow to make the process continuous and nearly fullyautomatic. For instance, several reaction vessels can be arranged inseries, whereby the sodium amalgam is passed to these reaction vesselseither concurrently or counte-rcurrently to the galliumatecontainingsodium aluminate solution so that a complete utilization of the amalgamis assured. The gallium-containing amalgam is then withdrawn from thelast reaction vessel and gallium is extracted therefrom and subsequentlyelectrolytically precipitated in conventional manner. The sodium amalgamis then again enriched with sodium and returned to the reaction vesselsfor extracting gallium from subsequent portions of the aluminatesolution.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic representation of an arrangement for the recoveryof gallium in accordance with the present invention;

FIG. 2 is an elevational view partially in cross section of a preferredembodiment of a reaction chamber for withdrawing gallium from. thesolution under formation of gallium amalgam and of separating means forseparating'amalgam from the gallium-poor solution leaving the reactionchamber;

FIG. 3 is a schematic elevational cross sectional view on a somewhatlarger scale of the reaction chamber shown in FIG. 2; and

FIG. 4 is a cross sectional plan view taken along line IV-IV of FIG. 3.

Referring now to FIG. 1, it 'will be seen that the arrangement accordingto the present invention comprises a reaction chamber 1 and a separatingdevice 2 superposed upon reaction chamber 1 and combined with the sameinto a unitary structure.

Reaction chamber 1 serves for reacting, with liquid sodium amalgam, forinstance, gallium-containing sodium aluminate lye such as is obtained inthe Bayer process of bauxite decomposition, whereby gallium will bedissolved in the mercury of the sodium amalgam, forming gallium amalgam,or more accurately gallium-sodium amalgam, and in exchange sodium of thesodium amalgam will be withdrawn therefrom and dissolved in the sodiumaluminate lye.

Separating device 2 serves for separating by sedimentation amalgamparticles which were carried along by the aluminate lye from reactionchamber 1. According to the illustrated preferred embodiment, theseparated amalgam will flow downwardly along the inclined bottom ofseparating device 2, back into reaction chamber 1.

Conduit 3 leads from separating device 2 via pump 4 to the bottomportion of reaction chamber 1. Clear sodium aluminate lye free ofamalgam passes through conduit 3 into the lower portion of reactionchamber 1 of the sodium of the amalgam will be dissolved in thealuminate lye and, in exchange, a portion of the gallium of thealuminate lye will form gallium amalgam. In order to obtain a largereactive contact area between the gallium-containing sodium aluminatelye and the sodium amalgam, the aluminate lye is pressed through nozzles5 into the liquid sodium amalgam filling the free space of reactionchamber 1.

Conduit 6 serves for introducing fresh gallium-containing aluminate lyeinto separating device 2, and con-v duit 7 which communicates with the.lower portion of separating device 2 serves for Withdrawinggallium-poor lye or solution from the gallium extracting arrangement.The sodium aluminate solution withdrawn through conduit 7, for instance,may be reintroduced into the aluminum oxide (Bayer) process.

When it is desired to carry out the gallium extraction in a continuousmanner, it is necessary to replenish the sodium content of the amalgamat regular intervals. For this purpose, the amalgam is withdrawn fromreaction chamber 1 through conduit 8 via pump 9 and introduced into aconventional electrolytic cell for the electrolysis of alkali metalchlorides. In this cell 10, the sodium content of the amalgam isreplenished and the thus reconstituted sodium amalgam is then returnedto reaction chamber 1 by way of conduit 11. However, it is also possibleto replenish the sodium content of the amalgam in a different manner,for instance, by adding sodium to the amalgam.

When the gallium content of the amalgam has risen to such an extent thatit is desirable to extract gallium therefrom, it is preferred towithdraw such amalgam of relatively high gallium content and low sodiumcontent through conduit 13 (in parallel to conduit 8) into extractionvessel 12. After separating gallium from the amalgam, the thus formedmercury, or sodium and gallium-poor amaglam, is then passed throughconduit 14 into electrolytic cell 10 for being enriched with sodium, andfrom there through conduit 11 back into reaction chamber 1. It is ofcourse, also possible to withdraw amalgam from the reaction chamber 1through conduit 8 and to pass part of the withdrawn amalgam directly toelectrolytic cell 10, and another part via extraction vessel 12 to cell10.

Gallium is then separated from the gallium-containing solution formed inextraction vessel 12 by electrolysis in electrolytic cell 15. Sometimesit is desirable to subject the gallium-containing solution formed inextraction vessel 12 to conventional purification steps prior tointroducing the solution into electrolytic cell 15.

FIG. 2 will serve to illustrate insome more detail the structure andoperation of the combined reaction and separating means.

Reaction chamber 1 is preferably of cylindrical configuration having aheight of between 200 and 1,000 mm., most preferably of about 500 mm.and a diameter of between 150 and 1,000 mm. The gallium-containingsolution is introduced into reaction chamber 1 through conduit 3 whichcommunicates with distribution chamber 16 arranged in the illustratedembodiment in the area of the upper end portion of reaction chamber 1,somewhat above the latter. Closed distribution chamber 16 communicateswith a plurality of downwardly extending ducts 17 which terminate in thelower portion, near the bottom of reaction chamber ,1. Preferably, thereare arranged between 3 and 20, most preferably about 10 ducts per cm. ofthe horizontal cross sectional area of reaction chamber 1, and each ofducts 17 preferably has a diameter of about 20 mm. Ducts 17 are immersedat least throughout most of their length in the sodium amalgam fillingthe remaining free space in reaction chamber 1. The gallium-containingclear sodium aluminate lye or the like flow-s under pressure throughconduit 3 into distribution chamber 16 and from there through ducts 17to the lower portion of reaction chamber 1. The lower ends of ducts 17carry a nozzle arrangement 5 through which the gallium-containingsolution is pressed in finely subdivided form into the liquid amalgamsurrounding ducts 17. Nozzle arrangement 5 will also serve to prevententry of amalgam into ducts 17.

The hourly yield of this apparatus, under otherwise.

equal conditions, will depend on the amount of amalgam introduced intoreaction .chamber 1. Since the height of the amalgam column iscontrolled by the height of reaction chamber 1, the hourly capacity canbe increased by increasing the diameter of reaction chamber 1.

During the turbulent upward passage of the galliumcontaining solutionthrough the liquid amalgam in reaction chamber 1, a portion of theamalgam will be carried along in the form of fine droplets intoseparating device 2. In separating device 2, .these fine amalgamdroplets will flow downwardly by force of gravity and by suchsedimentation eventually will flow along the inclined bottom ofseparating device 2 back into reaction chamber 1. In order to facilitateand speed up the flow of amalgam droplets along the inclined bottom ofseparating device 2, it is desirable to arrange a suitable stirring ap-'7 paratus (not shown) in separating device 2. Foam formed during thereaction between gallium-containing solution and amalgam will accrue onthe free upper surface of the gallium-containing solution in separatingdevice 2 and will disintegrate.

According to the embodiment of FIG. 2, the clear solution will flow fromseparating device 2 through outlet tube 18 into conduit 3 via pump 4 anddistribution chamber 16 into reaction chamber 1. Conduit 3 preferably isarranged as a circular conduit communicating with a plurality of outlettubes 18. The speed with which the solution is circulated from reactionchamber 1 to separating device 2 and back to reaction chamber 1 willdetermine the efficiency and yield of the gallium separation. If thespeed is chosen too low, the circulation will be too slow for optimumgallium-sodium exchange, and if the circulating speed is too high, toomuch of the amalgam will be carried upwardly into separating device 2.

Experiments have shown that very good results are achieved bycirculating an amount of solution which is equal to between 0.2 and 2liters per minute, preferably about 1 liter per minute, multiplied bythe number of ducts 17.

Heat created by the gallium-sodium exchange will cause a reduction inyield. In view thereof, it is desirable to provide separating device 2with a cooling jacket 19 which will serve the double purpose of coolingthe solution contained in separating device 2 and also cooling solutionflowing through a portion of outlet tubes 18 which is located withincooling jacket 19. In this manner, the solution entering reactionchamber 1 can be cooled sufiiciently to prevent undue heating up of thereaction mixture in reaction chamber 1. The cooling water enters jacket19 through inlet 20 and is withdrawn through outlet 21. The greater thenumber of outlet tubes 18 located in part within cooling jacket 19, thebetter will be the cooling efiect. Conduit 8 serves for withdrawingamalgam of reduced sodium content from reaction chamber 1, for furtherprocessing as discussed in connection with FIG. 1. Preferably aconventional mercury cup-and-cone arrangement (not shown) is arranged inconnection with outlet 8 to prevent carrying along of solution with thewithdrawn amalgam.

The replenished sodium amalgam is then reintroduced into reactionchamber 1 through conduit 11, as more fully described in connection withFIG. 1.

Reaction chamber 1 and separating device 2 may be built of iron.Distribution chamber 16 may consist, for instance, of iron or syntheticmaterial.

' More specifically, reaction chamber 1 may be constructed asillustrated in FIG. 3. The solution introduced through conduit 3 ispressed by pump 4 into the continuation or riser 3' of conduit 3 whichcommunicates with closed distribution chamber 16 from which the solutionis then pressed downwardly through ducts 17 and after passing throughnozzles 5, the solution will thus be pressed in finely subdivided forminto the amalgam surrounding ducts 17. Amalgam is introduced throughconduit 11 and is withdrawn through outlet 8. After circulating asdescribed in connection with FIGS. 1 and 2, a portion of the solution,or the gallium-poor solution, is withdrawn through conduit 7.

FIG. 4 shows the upper opening of conduit 3' through which the solutionenters distribution chamber 16, and of ducts 17 through which thesolution passes downwardly from distribution chamber 16 into contactwith the amalgam in the lower portion of reaction chamber 1.

The diameter of nozzles 5 preferably will be about 2 mm. and usuallywill be between 1 and 3 mm. Assuming that the mercury, i.e. amalgamcolumn in reaction chamber 1 has a height of 500 mm., the pressureexerted by pump 4 preferably will be 1 atmosphere above atmosphericpressure. This pressure is not directly proportional to the height ofthe amalgam column. For instance, in case the amalgam column has aheight of 1,000

mm., it will suflice to supply a pressure of 1.7 atmospheres aboveatmospheric pressure since the resistance offered by the conduit andducts does not change materially by such increase in the height of theamalgam column.

The cross sectional area of conduit 3 preferably is at least equal toand up to twice the cross sectional area of riser 3, and the sum totalof the cross sectional areas of all ducts 17 preferably will be aboutequal to the cross sectional area of riser 3'.

The entire free space in reaction chamber 1 is filled with amalgam.According to FIGS. 2 and 3 conduit 8 for withdrawal of amalgamcommunicates with reaction chamber 1 at about one-half the height of thelatter because at that point amalgam will be withdrawn having a goodaverage content of gallium. Care must be taken that reaction chamber 1will remain filled with amalgam, notwithstanding the withdrawal of aportion thereof through conduit 8. This may be achieved, for instance byarranging electrolytic cell 10 at a level corresponding to the upperlevel of amalgam which is to be maintained in reaction chamber 1.

Referring again to the drawings, the arrangement according to thepresent invention may be operated by introducing gallium-containingsodium aluminate lye according in the Bayer aluminum oxide processthrough a conduit 6 into separating device ZWhich is arranged above andunitary with reaction chamber 1. The thus introduced aluminate lye plusalready reacted solution of reduced gallium content is then passedthrough conduit 3 and pump 4 in finely subdivided form into the liquidsodium amalgam located in reaction chamber 1, and will react therewith.Solution of reduced gallium content carrying along droplets of amalgamwill pass upwardly into separating device 2. The carried along amalgamwill flew back into reaction chamber 1, and after repeated circulation,the gallium-poor solution which is free of amalgam will be returned tothe Bayer process through conduit 7 and will accept additional sodiumgalliumate before being returned through conduit 6 into separatingdevice 2. The gallium enriched amalgam of reduced sodium content, or aportion thereof is extracted in extraction vessel 12 and then againenriched with sodium in electrolytic cell 10. Another portion of thesodiumdepleted amalgam may be enriched in electrolytic cell 10 withoutfirst passing through extraction vessel 12. The sodium enriched amalgamis returned to reaction chamber 1 through conduit 11 while the separatedgallium-containing solution formed in extraction vessel 12, preferablyafter purification, is subjected to electrolytic separation of galliumin cell 15.

The following examples are given as illustrative only without, however,limiting the invention to the specific details of the examples.

Example I 2 liters of sodium aluminate solution as it accrues in thedecomposition of bauxite and containing about 290 g. sodium oxide perliter and 300 mg. gallium oxide (Ga O are treated with 1,000 g. ofsodium amalgam containing about 0.2% sodium. The amalgam drops into thevessel containing the sodium aluminate solution through a plurality ofnozzles so that thin threads of amalgam are formed which separate intoindividual droplets. These droplets pass downwardly through the sodiumaluminate solution and collect on the bottom of the vessel from wherethe amalgam is recycled to the nozzles and again introduced into thesodium aluminate solution. Within 1 hour, the gallium content of thesolution has dropped by 30 mg. per liter while the sodium content of thesodium amalgam has been reduced to about 0.02%.

Example II 2 liters of the sodium aluminate solution described inExample I are treated with 8,000 g. of sodium amalgam sodium content ofthe amalgam has been lowered to It is desirable to proceed -inaccordance with Example I when gallium has to be recovered from arelatively large volume of sodium aluminate solution with the use of arelatively small quantity of mercury. The initial sodium content of theamalgam can be considerably higher than the percentage figures indicatedabove and in this manner, the quantity of mercury required for recoveryof gallium can be further reduced.

The conditions of Example II are representative of the process when arelatively small quantity of gallium-containing sodium aluminatesolution is to be treated in such a manner as to obtain a high yield ofrecovered gallium. Duration of the process which has been described asAluminate Solution Containing:

130 g./l. A1 260 g./l. NaiO 270 mgJl. GanOs 1O l./h.

270 mg./l. G340;

between 1 and 3 hours can be further reduced by reducing the size of theindividual mercury droplets, i.e. by increasing the amalgam surface areawhich will be in contact with the gallium-containing aluminate solution.

The recovery of gallium from the sodium amalgam is carried out inconventional manner, preferably by washing the amalgam with nitric acid,however, it is also possible to subject the gallium-containing sodiumamalgam to extraction with sodium hydroxide, 'a process which also isknown in the art.

Preferably, particularly in large scale industrial installations, thegallium-containing amalgam of reduced sodium content which collectsat-the bottom of the reaction vessel will first be passed to aconventional sodium amalgam producing electric cell and therein will beenriched with sodium. From the sodium enrichment cell, the amalgam isthen pumped again to the nozzles from which it drops into the sodiumaluminate solution.

The gallium-containing sodium aluminate solutions which may be treatedaccording to the present invention may either be sodium aluminatesolutions as they are obtained by decomposition of bauxite, i.e. sodiumaluminate solution containing a high percentage of aluminum oxide or themother liquor which remains after crystallization and separation-ofaluminum hydroxide, i.e. a solution which contains only a relativelysmall percentage of aluminum oxide. Since the galliumate which isintroduced into the solution during the decomposition of the bauxitewill not precipitate together with aluminum hydroxide, the galliumatewill be found in the aluminate solutions before as well as afterprecipitation of aluminum hydroxide and can be extracted with sodiumamalgam from solutions of high aluminum oxide concentration as well asfrom solutions of low aluminum oxide concentration.

Example III A continuous manner of carrying out the process of thepresent invention is illustrated in the following flow diagram:

Bauxite Containing: 0.005%

Buyer process (decomposition of bauxite to partial evaporation ofsolution) 130 g. [1.11 03 260 g./l. Na o 300 mg./1. G820;

Reaction vessel Electrolytic cell 12 kg./h. Hg

0.15%; Na l Up to between 0.5-0.1% Ga During operation of the process asschematically shown portion of the amalgam flowing towards theelectrolytic cell, extracting gallium and other elements contained inthe sodium amalgam therefrom, for instance with nitric acid, and thenreturningthe thus treatedportion of the sodium amalgam to theelectrolytic cell in which the sodium content of the amalgam isrestored.

Generally, the sodium aluminate solutions of the Bayer process which aretreated in accordance with the present 1 1 invention will have acomposition within the following ranges:

The maximum sodium content of the sodium amalgam depends on theoperating temperature and will range from about 0.35% to 2%. The minimumsodium concentration at which for practical purposes gallium separationwill substantially come to halt is about 0.001%. Generally, the processis carried out at ambient temperatures of between about 15 and 20 C. andunder such conditions, the maximum sodium content of the amalgampreferably will be 0.2% and the minimum content 0.02%. In any event, thesodium content of the amalgam will be so chosen that the amalgam iscapable of forming droplets, i.e., is liquid at the temperaturesprevailing during the process.

are treated with 1,000 g. sodium amalgam containing 0.2% sodium.

The sodium al-uminate solution is contained in a cylindrical vesselforming therein a liquid column of about 60 mm. diameter and 75 cm.height. The sodium amalgam is introduced through nozzles arranged abovethe vessel and evenly distributed over the cross section of the same,each nozzle having a diameter of 1 mm. The amalgam drops into the columnof liquid and collects at the bottom of the vessel from where theamalgam is pumped back to the nozzles. The amalgam circulates between 50and 70 times per hour. Already after 1 hour, the gallium content of thesolution has dropped to :22 g./l. and the composition of the solution isnow as follows:

The sodium content of the amalgam is now 0.02% and the gallium content0.01%.

Example V 2 liters of Bayer process aluminate solution of thecomposition described in Example IV are treated with 8,000

g. of sodium amalgam containing 0.2% sodium for a period of 3 hours inthe manner described in Example IV. At the end of the 3-hour treatment,it is found that the aluminate solution has the following composition:

A1 0 Na O free 266 Na O tOtal 63203 sio 1.2 ZnO CI'203 F6203 M003 V O P0 and the amalgam contains:

Percent Ga 0.0045 Zn 0.002

As described further above, it is desirable to provide the largestpossible contact area between amalgam and aluminate solution.Preferably, the amalgam is broken up into droplets having a diameter ofbetween 0.15 and 1.5 mm. This can be accomplished by pressing theamalgam through nozzle orifices having a diameter of between 0.1 and 1.0mm. After passing through the nozzle orifices, the amalgam threads breakup into droplets of the above diameters.

Thus, according to the present invention, gallium can be separated fromalkaline solutions containing the same, by reacting thegallium-containing solution with sodium amalgam so that a portion of thesodium of the amalgam will be transformed into sodium hydroxide, thusincreasing the content of free Na 0 of the solution, while the galliumwill be taken up by the amalgam. The process can be easily carried outin a continuous manner by circulating sodium amalgam through thegallium-containing solution while continuously replacing part of thetreated solution with fresh solution, and part of the gallium-containingamalgam with amalgam from which gallium has been separated. Furthermore,the sodium content of the circulating amalgam is preferably replenishedafter the amalgam has been withdrawn from the solution and before it isreintroduced into the same, in order to compensate for the loss ofsodium in the form of sodium hydroxide going into the solution.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

, What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of recovering gallium from an aqueous alkaline solutioncontaining aluminum in the form of a dissolved aluminate and gallium inthe form of a dissolved galliumate, the step of reacting said solutionwith droplets of a liquid alkali metal amalgam so as to selectivelyreduce at least a portion of said gal'liumate to metallic gallium whilesaid aluminate will remain unaffected, said metallic gallium'being takenup by said amalgam, and simultaneously transforming a portion of thealkali metal of said amalgam into the hydroxide of said alkali metal,the thus-formed hydroxide being incorporated in said solution, wherebygallium is recovered from said solution in the fiorm of gallium amalgam.

2. In a method of recovering gallium froman aqueous alkaline solution ofan aluminate and a galliumate, the steps of reacting said solution at atemperature of between about 15 and 20 C. with liquid sodium amalgamcontaining between about 0.02% and 0.2% sodium so as to selectivelyreduce at least a portion of said galliurnate to metallic galliumwithout alfecting said aluminate, said metallic gallium being taken upby said amalgam and simultaneously transforming a portion of the alkalimetal of said amalgam into the hydroxide of said alkali metal, thethusformed hydroxide being incorporated in said solution; and separatingthe thus formed gallium-containing amalgam from said solution, wherebygallium is recovered from said solution in the form of gallium'amalgam.

3. A method of recovering gallium from an aqueous alkaline solution of arelatively large proportion of sodium aluminate and a relatively smallproportion of sodium galliumate, comprising the steps of reacting saidsolution with liquid sodium amalgam containing between about 0.001% and2% of sodium so as to selectively reduce at least a portion of saidgalliumate to metallic gallium without afiecting said aluminate, saidmetallic gallium being taken up by said amalgam and simultaneouslytrans-forming a portion of the sodium of said amalgam into sodiumhydroxide, the thus-formed hydroxide being incorporated in saidsolution; separating the thus-forrned gallium-contain- .ing amalgam fromsaid solution; and separating gallium from said amalgam, whereby galliumis recovered from containing between about 0.001% and 0.35% of sodium sothat selectively at least a portion of the gallium of said galliumate ofsaid solution is taken up by said amalgam in exchange for a portion ofthe sodium thereof.

5. In a method of recovering gallium from an aqueous sodium aluminatesolution containing a relatively small proportion of sodium galliumatethe steps of reacting said solution with liquid sodium amalgam adaptedto form droplets and containing between 0.001% and 2% of sodium so as toselectively reduce without affecting said aluminate at least a portionof said galliumate to metallic gallium, said metallic gallium beingtaken up by said sodium amalgam, while simultaneously transforming aportion of the sodium of said sodium amalgam into sodium 7 hydroxide andincorporating the thus-formed sodium hydroxide into said solution; andseparating the thus formed gallium-containing'amalgam from saidsolution.

6. In a method of recovering gallium from bauxite containing the same,the steps of digesting the bauxite With caustic soda so as to form analkaline aqueous sodium aluminate and sodium galliumate-containingsolution, contacting said solution with liquid sodium amalgam adapted to:form droplets and containing up to 2% of sodium so as to selectivelyreduce without affecting said aluminate at least a portion of thedissolved galliumate to metallic gallium, the latter being taken up bysaid sodium amalgam, while simultaneously incorporating a portion of thesodium of said sodium amalgam into said solution in the form of sodiumhydroxide; and separating the thusformed gallium-containing sodiumamalgam from said solution.

7. A method of recovering gallium from an aqueous alkaline solution of arelatively large proportion of sodium aluminate and a relatively smallproportion of sodium galliumate, comprising the steps of reactingsubdivided droplet-forming liquid sodium amalgam with said solution soas to selectively reduce without affecting said aluminate at least aportion of said dissolved galliumate to metallic gallium, the latterbeing taken up by said sodium amalgam, while simultaneouslyincorporating a portion of the sodium of said sodium amalgam into saidsolution in the form of sodium hydroxide; separating the thus-formedgallium-containing sodium amalgam from saidsolution; and recoveringmetallic gallium from said amalgam.

8. A continuous method of recovering gallium from an aqueous sodiumaluminate solution having a sodium oxide content of between about and300 grams perliter and containing a galliumate in a concentration beinga fraction only of the concentration of said sodium aluminate in saidsolution, comprising the steps of circulating through said solutiondroplets of liquid sodium amalgam containing between about 0.001% and 2%of sodium so as to selectively reduce without afiecting said aluminateat least a portion of said galliumate to metallic gallium said metallicgallium being taken up by said sodium amalgam, while simultaneouslytransforming a portion of the sodium of said sodium amalgam into sodiumhydroxide and incorporating the thus-formed sodium hydroxide into saidsolution; separating said gallium-containing amalgam from said solution;recovering at least the major portion of said gallium from said amalgam;reconstituting the initial sodium content of said amalgam; andreintroducing said reconstituted amalgam of reduced gallium content intosubsequent portions of gallium-containing aluminate solution.

9. A method of recovering gallium from an aqueous alkaline solutioncontaining a relatively large proportion of sodium aluminate and arelatively small proportion of sodium galliumate, comprising the stepsof reacting droplets of liquid sodium amalgam having a diameter ofbetween about 0.15 and 1.5 mm. with said solution so as to selectivelyreduce without aifecting said aluminate at least a portion of saiddissolved galliumate to metallic gallium, the latter being taken up bysaid sodium amalgam, while simultaneously incorporating a portion of thesodium of said sodium amalgam into said solution in the form of sodiumhydroxide; separating the thus-formed gallium-containing sodium amalgamfrom said solution; and recovering metallic gallium from said amalgam.

10. A continuous method of recovering gallium from an aqueous sodiumaluminate solution having a sodium oxide content of between about 120and 300 grams per liter and containing a relatively small proportion ofsodium galliumate, comprising the steps of circulating through saidsolution droplets of liquid sodium amalgam containing between about0.001% and 2% of sodium so as to selectively reduce without affectingsaid aluminate at least a portion of said. .galliumate to metallicgallium said metallic gallium being taken up by said sodium amalgam,while simultaneously transforming a portion of the sodium of said sodiumamalgam into sodium hydroxide and incorporating the thus-formed sodiumhydroxide into said solution; separating said gallium-containing amlagamfrom said solution; recovering gallium from said amalgam;

increasing the sodium content of said amalgam; and reintroducing thethus-formed amalgam of increased sodium and reduced gallium content intosubsequent portions of gallium-containing aluminate solution.

11. A method of recovering gallium from the aqueous sodium aluminatesolution obtained by decomposition of bauxite in accordance with theBayer process which solution contains a relatively high proportion ofalumina and a relatively small proportion of sodium galliumate,comprising the steps of reacting said solution with liquid sodiumamalgam adapted to form droplets and containing between about 0.001% and2% of sodium so as to selectively reduce without alfecting saidaluminate at least a portion of said galliumate to metallic gallium,said metallic gallium being taken up by said sodium amalgam whilesimultaneously a portion of the sodium of said sodium amalgam istransformed into sodium hydroxide and the thus formed sodium hydroxideis incorporated in said solution; separating said gallium-containingamalgam from said solution; and recovering gallium from said amalgam.

12. A method of recovering gallium from the aqueous mother liquorobtained after removal of the major portion of aluminum hydroxide fromthe solution formed by decomposition of bauxite in accordance with theBayer process, which mother liquor contains sodium aluminate and sodiumgalliumate, comprising the steps of reacting said mother liquor withliquid sodium amalgam adapted to form droplets and containing betweenabout 0.001% and 2% of sodium so as to selectively reduce withoutaffecting said aluminate at least a portion of said galliumate tometallic gallium, said metallic gallium being taken up by said sodiumamalgam while simultaneously a portion of the sodium of said sodiumamalgam is transformed into sodium hydroxide and the thus formed sodiumhydroxide is incorporated in said mother liquor; separating saidgallium-containing amalgam from said mother liquor; and recoveringgallium from said amalgam.

13. A method according to claim 8 wherein sodium carbonate accruing inthe decomposition of bauxite in accordance with the Bayer process isused for reconstituting the initial sodium oxide content of saidsolution.

14. In a method of recovering gallium from an aqueous alkaline solutioncontaining aluminum in the form of a dissolved aluminate and gallium inthe form of a dissolved galliumate, the step of introducing saidsolution into a liquid alkali metal amalgam so as to selectively reduceat least a portion of said galliumate to metallic gallium while saidaluminate will remain unaffected, said metallic galliu-m being taken upby said amalgam, and simultaneously transforming a portion of the alkalimetal of said amalgam into the hydroxide of said alkali metal thethusformed hydroxide being incorporated in said solution, wherebygallium is recovered from said solution in the form of gallium amalgam.

15. In a method of recovering gallium from an aqueous alkaline solutioncontaining aluminum in the form of a dissolved aluminate and gallium inthe form of a dissolved galliumate, the step of introducing underpressure a plurality of relatively thin streams of said solution into aliquid alkali metal amalgam so as to selectively reduce at least aportion of said galliumate to metallic gallium while said aluminate willremain unaflected, said metallic gallium being taken up by said amalgam,and simultaneously transforming a portion of the alkali metal of saidamalgam into the hydroxide of said alkali metal the thusformed hydroxidebeing incorporated in said solution, whereby gallium is recovered fromsaid solution in the form of gallium amalgam.

References Cited by the Examiner UNITED STATES PATENTS 5/1957 Breteque204-105 3/1960 Cunningham 108 OTHER REFERENCES DAVID L. RECK, PrimaryExaminer.

BENJAMIN HENKIN, Examiner.

1. IN A METHOD OF RECOVERING GALLIUM FROM AN AQUEOUS ALKALINE SOLUTIONCONTAINING ALUMINUM IN THE FORM OF A DISSOLVED ALUMINATE AND GALLIUM INTHE FORM OF A DISSOLVED GALLIUMATE, THE STEP OF REACTING SAID SOLUTIONWITH DROPLETS OF A LIQUID ALKALI METAL AMALGAM SO AS TO SELECTIVELYREDUCE AT LEAST A PORTION OF SAID GALLIUMATE TO METALLIC GALLIUM WHILESAID ALUMINATE WILL REMAIN UNAFFECTED, SAID METALLIC GALLIUM BEING TAKENUP BY SAID AMALGAM, AND SIMULTANEOUSLY TRANSFORMING A PORTION OF THEALKALI METAL OF SAID AMALGAM INTO THE HYDROXIDE OF SAID ALKALI METAL,THE THUS-FORMED HYDROXIDE BEING INCORPORATED IN SAID SOLUTION, WHEREBYGALLIUM IS RECOVERED FROM SAID SOLUTION IN THE FORM OF GALLIUM AMALGAM.